The present invention relates to a system having a single manually operated lever for controlling more than one continuously variable parameter. The particular application described here is the control of more than one proportional hydraulic valve in an agricultural tractor.
As is well known, agricultural tractors usually have two or more hydraulic outlets to which agricultural implements having hydraulically powered functions may be connected. For example, a large reversible xe2x80x9csemi mountedxe2x80x9d plough would have a hydraulic cylinder for raising and lowering the plough on its support wheel, and also a hydraulically driven mechanism for reversing the orientation of the plough at each headland turn. Both of these functions would be powered from xe2x80x9cauxiliaryxe2x80x9d hydraulic outputs on the tractor, and would be initiated and controlled by the operator from the tractor cab.
As many as six or more of these auxiliary outputs may be provided on the tractor and controlling the output at all of them so that the implement or implements attached to the tractor are correctly controlled can be difficult. Since the operations, eg for the above described plough, are often repetitive it is essential to make control of the supply to these outputs as convenient as possible to reduce operator fatigue.
It is known to have an electronic control system including continuously adjustable manual control members in the tractor cab for adjusting the setting of respective electro-hydraulic valves. Normally, the control members are continuously adjustable from a neutral position to a xe2x80x9cmaximum flowxe2x80x9d setting in either direction from the neutral position. The control member may have to be moved against a spring to put it into a maximum flow setting, and the flow may be held at the maximum for a predetermined interval of time after the member has been released from the maximum flow position. The value of xe2x80x9cmaximumxe2x80x9d flow may sometimes be preset using some other input means.
According to present invention an electronic control system is provided according to claim 1 hereto. The operator need only hold a single control lever or xe2x80x9cjoystickxe2x80x9d to control several parameters, eg the settings of auxiliary hydraulic outputs on a tractor. One parameter (hydraulic output) may be adjusted to a desired value and then the lever moved to a different parallel slot to adjust another parameter (hydraulic output).
Preferable features are set out in the dependent claims. The advantages of these and other features will be apparent from the following description of one specific embodiment of the invention. The description is given by way of example only, with reference to the accompanying drawings.